Furans as Versatile Synthons: Total Syntheses of Caribenol A and Caribenol B

Two complex norditerpenoids, caribenols
A and B, were accessed from a common building block. Our synthesis
of caribenol A features the diastereoselective formation of the seven-membered
ring through a Friedel–Crafts triflation and a late-stage oxidation
of a furan ring. The first synthesis of caribenol B was achieved using
an intramolecular organocatalytic α-arylation. An unusual intramolecular
aldol addition was developed for the assembly of its cyclopentenone
moiety, and the challenging trans-diol moiety was
installed through a selective nucleophilic addition to a hydroxy 1,2-diketone.
Our overall synthetic strategy, which also resulted in a second-generation
synthesis of amphilectolide, confirms the usefulness of furans as
powerful nucleophiles and versatile synthons.